The circadian timing system, which strongly influences the occurrence and quality of sleep, is altered significantly with aging. Both the phase and amplitude of rhythms may undergo age-related changes. Due in large part to this breakdown, or fundamental change, in the circadian systems of the elderly, sleep disturbance is common among people over 65 years of age. Up to half of the population over 65 suffers from chronic sleep disturbance. The magnitude of the problem is emphasized by the fact that approximately 40% of hypnotic medications are prescribed to people over 60 years of age, and this proportion increases with age. The changes in sleep associated with normal aging are exacerbated in geriatric depression, the most common psychiatric disorder affecting the elderly. Such sleep disturbance may further compromise cognitive function that is already impaired by the depression. Additionally, sleep disturbance in geriatric depression presents a special challenge to caregivers at home and in institutional settings. The use of medications to treat sleep disturbance in the elderly is complicated by a number of factors, including hangover effects, tolerance and interactions with other medications. Timed exposure to bright .light represents an effective treatment alternative for sleep maintenance difficulties, at least in the short term, in generally healthy older subjects. Based on the success of our original work, it is proposed here to take the logical next steps in developing this promising, non-drug treatment for age-related sleep disturbance. In the abstract of our original study, it was suggested that the study would "form the basis for subsequent investigations to evaluate: (a) the long-term effectiveness of bright light therapy in controlling sleep disturbance and enhancing quality of life and health in the elderly, and (b) the application of these approaches to other clinical conditions and settings." The current application addresses these two important issues. The study will employ objective, physiological measures to track response to bright light treatment over a period of three months in a group of healthy elderly subjects and a group of elderly, depressed out patients. A separate group of healthy elderly will be studied in a control condition. By studying healthy, sleep disturbed elderly for a period of three months, it will be possible to assess the long-term efficacy of the bright light treatment. Moreover, by designing and testing a less-restrictive treatment schedule, it will be possible to determine the feasibility, and acceptance by subjects, of longterm treatment regimens. Finally, the inclusion of a group of geriatric depressed patients will make it possible to evaluate the efficacy of timed exposure to bright light in subjects with a disorder that is often characterized by severe sleep disturbance of the type shown to be responsive to this intervention.